Mosfet Circuit

In many applications, it`s desirable to disable LEDs used for system verification. Many options are available for the disabling function, including manual SPST (single-pole single-throw) switches, enhancement- and depletion-mode MOSFETs, bipolar-junction transistors, and JFETs. The circuit in Figure 1 automatically disables the LEDs when a mechanical housing encloses the circuit card, thereby preventing you from accidentally leaving the LEDs on to waste power...

Modern electronic ballasts require added features, such as high-frequency preheat for filaments, nominal lamp-power control, and light-dimming capability. Because the output inverter operates in resonant mode, you can control the power or current of these ballasts simply by varying the switching frequency. To vary the frequency, you can build a simple VCO that uses a half-bridge MOSFET driver (Figure 1). You can use this VCO as the core of a controller for a supply or ballast that requires a variable frequency...

In this circuit the switches are power MOSFETs driven to conduct alternately by windings on a current transformer. The primary of this transformer is driven by the current in the lamp circuit and operates at the resonant frequency of L-C. Unfortunately, the circuit is not self starting and must be pulsed by the DIAC connected to the gate of the lower MOSFET...

A zero-voltage-switching (ZVS) controller usually integrates a one-shot circuit, embodied in a VCO system. An error amplifier monitors the output voltage and adjusts the VCO`s off-time to keep the output value at a constant level. Each on-time period commences as soon as the primary voltage drops to zero, thus eliminating on/off commutation losses associated with the switching element. The controller also incorporates other convenient features, such as MOSFET drivers, a voltage reference, and overvoltage and undervoltage lockouts. In low-cost circuits, such a complex architecture can lead to a prohibitive cost, especially if you don`t need the cited features (in open-loop systems, for instance). Figure 1 shows an 8W, ZVS fluorescent-lamp converter made from two low-cost ICs, a CD4538 and an LM393...

Sensitive systems, such as those in aircraft, must withstand fault conditions, thereby avoiding component and system damage, because a sensor failure could cause a catastrophic event to occur. A channel protector, comprising two n-channel MOSFETs connected in series with a p-channel MOSFET, can protect sensitive components from voltage transients in the signal path, whether or not the power supplies are present (Figure 1)...

High Quality simple design No need for a preamplifier Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need...

The new LTC1155 Dual Power MOSFET Driver delivers 12V of gate drive to two N-channel power MOSFETs when powered from a 5V supply with no external components required. This ability, coupled with its micropower current demands and protection features, makes it an excellent choice for high side switching applications which previously required more expensive P-channel MOSFETs...

The circuit, which operates from a car battery, can charge a battery comprising one to six cells. IC1 is a buck-mode switching regulator that controls the external power switch, Q1, and the synchronous rectifier, Q2. These n-channel MOSFETs are more efficient than equivalent p-channel types, because the n-channel devices` on-resistance is lower, and they thus drop less voltage when conducting a given amount of current. IC1 includes a charge pump for generating the positive gate-drive voltage that Q1 requires...

The circuit`s 90% conversion efficiency offers a distinct power-saving advantage over resistor-limited and linearly regulated designs. It might appear that a series-LED connection is unsuitable for applications in which some (but not all) LEDs must be off. A cell phone, for example, sometimes needs that capability for occasions when the display is off but the keypad remains lit. Or, a PDA might need to play a sound file while maintaining illumination in the buttons but not the display. In the circuit of Figure 1, switching off individual LEDs or groups of LEDs is not a problem, even with series drive. Applying a logic-high level to the gate of a simple MOSFET switch, Q2, turns off a subset of LEDs by shunting their current. The remaining LEDs (for the keypad, for example) remain on, and their intensity remains constant because IC1 regulates their current, by sensing the voltage across R2 (300 mV at full brightness)...

This deceptively simple sequencer actually pulse width modulates the LEDs as it fades from one LED to the next. Bulbs will last much longer when driven in this gentle manner. Add MOSFETs or transistors to the outputs if you wish to drive bulbs. You can reconfigure the three capacitors from a wye configuration to a delta configuration, or you can remove one of them entirely and the circuit will still function. Use high efficiency LEDs for best results. This circuit was inspired by the BEAM sequencer circuits on the web. I simply reversed the roles of the resistors-capacitors and `floated` the capacitors. If you remove the 1nF capacitor then the resulting monstrosity will chirp out RF interference as it hobbles along...

Figure 1 presents an alternative to the typical boost power regulator. A buck-converter IC, IC1, generates the higher voltage that the white-light LED needs. An internal buck power stage connects between VIN and PGND, sourcing current to output Pin L. This circuit operates by turning on the high switch, thereby connecting the battery voltage across inductor L1. Once inductor L1 stores sufficient energy, the high-side switch turns off. The inductor current drives the switching node negative, and energy transfers through the low side into output capacitor C1, creating an essentially lossless switching event. Also, because the high- and low-side switches are MOSFETs, voltage drop is lower than that of a diode implementation; therefore, efficiency can be high...

With the improvement in high power MOSFETs of late lower gate charge, low loss gate structures, and much improved frequency capability it has become more possible to employ these switchmode devices in rf generators at medium hf. The objective is to improve the power density (W/m3) and efficiency of the equipment. The most common problem associated with this application is getting the matching right...

The circuit was designed and sold as a card by a purveyor of surplus components but, even using mostly manufacturer`s rejected transistors, we managed to get about 0.02% total harmonic distortion at 30 watts with a ±25v power supply into 8 ohms.: no bad figure even in these days of MOSFET and ICs...

Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need...

To celebrate the hundredth design posted to this website, and to fulfil the requests of many correspondents wanting an amplifier more powerful than the 25W MosFet, a 60 - 90W High Quality power amplifier design is presented here. Circuit topology is about the same of the above mentioned amplifier, but the extremely rugged IRFP240 and IRFP9240 MosFet devices are used as the output pair, and well renowned high voltage Motorola`s transistors are employed in the preceding stages...